The Complete Guide to Mobile App Localization (with a Checklist)

What is Mobile App Localization?

Mobile app localization is much more than simple text translation. It’s the process of adapting an app's content, design, and functionality to align with the language, culture, and technical standards of each target market. The goal is to create a user experience that feels completely native to your global audience, no matter their location.

Why Localize Your App?

Proper mobile app localization shows users they are seen and valued, which increases user satisfaction and engagement in new markets.

Localization Best Practices for Text and Design

1. Design for Text Expansion and Contraction

Different languages can significantly change text length (e.g., German often expands, Swedish contracts), which can break your layout.

Build adaptable designs to accommodate text variations and ensure proper handling of vertical scripts (like Korean) or right-to-left (RTL) languages (like Arabic or Hebrew).
Use Pseudolocalization as a testing method. This involves simulating text growth/shrinkage (e.g., 30% longer for German) to ensure translations won't break the UI before real translations are ready.

2. Tailor Content with Language and Locale Codes

Using a language code alone (e.g., fr for French) isn't enough. Regional differences significantly impact the user experience.

Use specific locale codes (e.g., fr_FR vs. fr_BE) to correctly tailor content elements like currency, time, and date formats.
Account for Plural Forms, as many languages have more than two forms (singular and plural) based on number ranges.

3. Provide Context for Linguists

Avoid the outdated practice of translating keys in a vacuum. Context is crucial for translation quality.

Use tools like Lang Q to allow linguists to translate one page at a time with screenshots, providing immediate context on where the text fits in the UI.
Preview translated text directly in the user interface to solicit feedback before production.

4. Maintain Consistency with a Glossary and Style Guide

A glossary and style guide are essential language assets. A glossary defines and describes key terminology, helping to keep translations consistent.

Use your TMS to set up a glossary, marking terms as translatable or case-sensitive.
The system should automatically highlight glossary terms in the editor to ensure linguists use the correct, approved terminology. This is vital in highly regulated industries.

Localization Best Practices for Images and Media

5. Keep Text External to Images

Avoid embedding text directly into images. Instead, use translatable text layers to simplify localization, allowing you to swap text easily without redesigning the visual.

If possible, use a TMS with Optical Character Recognition (OCR) or integration with design tools like Figma to manage text layers.
Provide your localization team with the source files for images, not just the final image format.

6. Test and Adapt Cultural Imagery

In some markets, you may need to swap or hide visuals based on the locale to test for and avoid cultural misunderstandings or inappropriateness. Design your app with this flexibility in mind.

Localization Best Practices for Development

7. Externalize Strings and Use Standardized Formats

Keep all text strings external to your code.
Use standardized file formats (e.g., JSON, XLIFF) for translation files. This streamlines updates, allows localization scaling, and avoids requiring code changes with every language update.
Use a tool that supports importing and exporting various file formats and integrates with major code repositories (like GitHub) for continuous updates.

8. Internationalize Time, Date, and Currency

The world is inconsistent with formatting. Make sure your code is built to handle:

Date Formats (month-first vs. day-first).
Time Formats (12-hour with AM/PM vs. 24-hour).
Currency Formats (symbols, decimal separators).

Refer to app internationalization (i18n) guidelines to ensure your code is globally ready from the start.

9. Merge Keys Across Multiple Platforms

When developing for platforms like iOS and Android, similar text often has different naming schemas (LoginButton vs. login_button).

By merging similar keys into a single entry in your TMS, you avoid repetitive translation tasks and keep your project clean.
Include all platform keys on export if you work with multiple platforms.

Localization Best Practices for Workflow

10. Accelerate Releases with Over-the-Air (OTA) Updates

OTA updates allow you to instantly publish and update text strings in your iOS and Android apps without resubmitting a new version to the App Store or Google Play.

Use a mobile Software Development Kit (SDK) like Lang Q's to deliver updates over the air.
This significantly speeds up your language rollout process, often making it faster than the app store review cycle.

11. Automate and Centralize Your Localization

Centralizing and automating your localization process ensures quality and speed by syncing tools with your codebase.

Set up automations to trigger updates, notifications, and even machine translations.
Implement a design-led localization workflow: use two-way integrations (e.g., between your TMS, GitHub, and Figma) to continuously sync content. This allows designers and developers to align efforts, embedding localization into the continuous deployment process.

12. Prioritize Early Localization Testing

Run localization tests early to catch layout or text expansion bugs before they reach production, which can reduce resolution costs by up to 10x.

Perform pre-production Quality Assurance (QA) for builds.
Use the Mobile SDK to push the latest translations to your pre-production environment, allowing QA teams to test in-app behavior, check UI/UX for specific languages, and ensure all keys are translated.

13. Localize Your App Store Metadata

Don't overlook App Store Optimization (ASO). Localizing metadata and keywords is crucial for discoverability and appeal in each new market.

Start by translating keywords, app name, description, and screenshots for as many locales as possible, even before in-app content is complete.
Tools like the Fastlane plugin can automate App Store and Google Play metadata updates.